Polyamide fibers stabilized with inorganic iodides and copper phthalates



lUnite Sttes 3 457,325 POLYAMIDE FIBERS STABILIZED WITH INGR- GANIC IODIDES AND CUPIPER PHTHALATES Anthony Anton, Wilmington, DeL, assignor to E. 1. du Pont de Nemours and Company, Wilmington, Deh, a corporation of Delaware N Drawing. Continuation-impart of application Ser. No. 438,071, Mar. 8, 1965. This appiication Apr. 14, 1967, Ser No. 630,812

Int. Cl. (108g 51/62, 41/02 US. Cl. 260-857 4 Claims ABSTRACT UP THE DISCLOSURE Synthetic linear polyamide fibers containing homogenously dispersed throughout 0.005 to 0.5% by weight of copper phthalate and 0.05 to 0.5% by Weight of an alkali metal iodide having improved resistance to heat degradation and degradation by ultraviolet radiation.

This application is a continuation-in-part of application Ser. No. 438,071, filed Mar. 8, 1965, now abandoned.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to improved heat stabilized synthetic linear polyamide fibers and spinning compositions for their production.

Description of the prior art Synthetic linear polyamide fibers are well known for their outstanding properties in end uses such as knitted and woven fabrics of various types. In recent years, meltspun polyamide yarns have come into wide-spread use in the reinforcement of pneumatic tires for automobiles and other vehicles. In this, as well as in other end uses, polyamide fiber are often subjected to high temperatures for extended periods of time. Under such conditions, the fiber tends to lose strength and become brittle unless a suitable stabilizing agent is added.

Polycarbonamide fibers modified by the presence of small amounts of copper compounds have been found to exhibit a remarkable resistance to degradation upon exposure to various atmospheric conditions, particularly exposure to high temperatures. However, in the preparation of these fibers, where the molten spinning composition is forced through a sand pack or similar device for filtration purposes and then extruded through a spinneret to form filaments which are subsequently quenched and processed into fibers, it has been found that the presence of copper compounds leads to an increased rate of plugging or loading of the sand pack. It is now recognized that cupric ions react with polycarbonamides, presumably with the free carboxyl groups present in the polymer. This may lead to the formation of gel particles or to reduction of the copper ions to form metallic copper particles which are insoluble in the polymer and which agglomerate to form particles of sufiicient size to be filtered out in the sand pack. The plugging of sand packs has been found to be particularly troublesome when the polycarbonamide is prepared either wholly or in part from an aromatic carboxylic acid.

Recently, it has been found that the plugging of sand packs may be substantially reduced if the copper is introduced as copper 8-hydroxyquinolate. The use of metal chelates of this type is described in U.S. Patent 3,272,773. While copper S-hydroxyquinolate, alone or in combination with an inorganic iodide, has proved satisfactory for for the stabilization of yarns to be used in the reinforcement of pneumatic tires, this stabilizer is unsuitable for polymer compositions to be used for textile proposes due 3,457,325 Patented July 22, 1969 to the development of a yellow color in the yarn so stabilized. Since the stabilizer is added prior to or during the polymerization process and since it is frequently desirable to use polymer from the same source for both tire yarn and textile end uses, it would be highly desirable to have a stabilizer which (1) provides adequate protection against heat degradation; (2) does not lead to plugging of the sand filters; and (3) does not develop any undesirable discoloration in the yarn.

SUMMARY OF THE INVENTION It has now been found that polyamide spinning compositions containing dispersed therein small amounts of copper isophthalate, copper orthophthalate or copper terephthalate in combination with an alkali metal iodide may be filtered without difiiculty due to excessive plugging of the sand filter and may be extruded to form filaments and yarn which are not discolored by the stabilizer. Fibers stabilized in the manner exhibit the desired resistance to heat degradation and are also resistant to degradation by ultraviolet radiation as is desirable in textile yarns.

For effective results at least 0.005% by weight of the copper orthophthalate, isophthalate or terephthalate based on the polymer weight should be employed in the polymer. While the upper concentration limit is not critical, generally no more than 0.5 of the copper salt will be found useful. The preferred range is 0.010.5%.

The iodide which is added to the polymer in conjunction with the copper salt is preferably sodium or potassium iodide since these are readily available and economical to use, however, any of the alkali metal iodides may be used if desired. The iodide should be used in a concentration of at least 0.05% based on the polymer weight. As in the case of the copper compound the upper concentration limit is not critical; however, generally no more than than 0.5 will be required and the preferred range is 01-03%.

For effective results, the copper salt and iodide must be dispersed throughout the polymer homogeneously. To accomplish this, these compounds must be added prior to or during the polmerization step or mixed with the molten polymer at some point prior to extrusion. As illustrated in Example III, coating the yarn with a stabilizing composition gives inferior results.

The stabilized fibers of this invention may be prepared from any polyamide such as, for example, those derivable from polymerizable monoarninocarboxylic acids or their amide-forming derivatives and those derived from the reaction of diamines with dicarboxylic acids or their amideforming derivativesln addition to those set forth in the examples, other suitable polyamides are those prepared from the polymers disclosed in US. Patents 2,071,253, 2,130,523, and 2,130,948. Interpolymers prepared from mixtures of diamines, dibasic acids, and amino acids can also be used for practice of this invention. Similarly, meltblends of two or more polyamides can be used if desired. A particular embodiment of this invention is a melt-blend of 90% by weight polyhexamethylene adipamide and 20-10% by weight of polyhexamethylene isophthalamide. In general, the range of polyamides which may be heat stabilized and which are adapted for use as reinforcement material or for textile purposes is well known. Specific polyamides which may be mentioned as suitable for use in the practice of this invention include polyhexamethylene adipamide, polyhexamethylene sebaccamide polymerized 6-amino-caproic acid, polytetramethylene sebacamide, polytetramethylene adipamide, polymetaxylene adipamide, the polyamide from bis(4-arninocyclohexyl)-methane and azelaic acid, sebacic acid, or decamethylene-l,10-di-carboxylic acid, and the polyamide from Z-methylhexamethylenediarnine and terephthalic acid. Specific copolymers which may be mentioned include the copolymer of polyhexamethylene adipamide and polyhexamethylene isophthaiimide or polyhexamethylene sebacamide, and the copolymer of polyhexamethylene adipamide and polyhexamethylene t-butyl-isophthalamide.

EXAMPLE I Description of preferred embodiments Copper isophthalate is prepared by adding 100 grams of solid isophthalic acid to 200 ml. of aqueous sodium hydroxide (29.3 grams NaOH/ 100 ml.) in a Waring Blendor, filtering the resulting solution, returning the filtrate to the blender and adding 200 ml. of aqueous copper chloride solution containing 78.5 grams of cupric chloride and filtering off the precipitated copper isophthalate. The precipitate is washed 5 times with distilled Water in the blender and dried overnight in a vacuum of 80 C.

Polyhexamethylene adipamide is prepared in an autoclave in the conventional manner from an aqueous salt solution containing 60% by weight of hexamethylene diammonium adipate. When the autoclave temperature reaches 150 C. at the beginning of the polymerization cycle, 469 grams of a aqueous potassium iodide solution is added for each 100 lbs. (45.36 kg.) of salt solution. When the temperature reaches 195 C., a 5% aqueous dispersion of copper isophthalate (101 grams of the suspension per 100 lbs. (45.36 kg.) salt solution is added. On completion of the polymerization cycle, the polymer is extruded, cooled, and cut into flake in the conventional manner. The flake which has a relative viscosity of 45 is then melted in a screw melter and pumped to a mixer where it is blended with by weight of polyhexamethylene isophthalamide supplied from flake melted in a separate screw melter and having a viscosity of 24. The blended polymer which contains 60 ppm. copper in the form of copper isophthalate and 0.2% by weight of potassium iodide is then passed at a rate of 2.0 lbs/hr. (0.9 kg./hr.) through a spinneret assembly having a V2" (1.27 cm.) diameter sand pack. The pack pressure increased 19.7 p.s.i./hr. per 1,000 p.s.i. initial pressure (1.38 kg./sq. cm./hr./ 70 kg. initial pressure) as compared to a rate of 37.6 psi. (2.64 kg./sq. cm.) for a similar polymer blend containing 60 ppm. copper in the form of copper acetate and 22.1 p.s.i. (1.55 kg./sq. cm.) for a polymer blend containing 60 ppm. copper in the form of copper 8-hydroxyquinolate in place of the copper isophthalate. All of the polymer blends contain 0.2% potassium iodide.

The extruded filaments are quenched, drawn, and wound into a yarn in the conventional manner. The yarn produced from polymer containing the copper isophthalate is almost white and can be bleached and dyed satisfactorily while that produced from polymer containing copper S-hydroxyquinolate has a yellowish cast and cannot be bleached or dyed satisfactorily. Samples of the yarn were placed in a forced air oven at 180 C. for varying periods of time and the tensile properties of the heat aged yarns determined. The yarn was held at constant length during the heat aging to prevent relaxation of the yarn. Results of this test together with comparative tests on yarn with no antioxidant and yarn with copper 8-hydroxyquinolate are shown in Table I below.

Yarn prepared as in Example I except that it contains ppm. copper in the form of copper isophthalate is exposed to an accelerated weathering test under a carbon arc in a commercially available tester known as the military Weather-Ometer. The tenacity loss after hours at 67.5 C. was 20% as compared to 68% for a similar sample containing no antioxidant. When a xenon arc, which gives radiation more nearly simulating sunlight, was used in the test, the yarn containing the copper isophthalate lost 18% of its tenacity after 980 hours as compared to 61% lost for the sample containing no antioxidant.

As shown in the foregoing examples, the polymer composition containing the copper isophthalate dispersed therein is at least equivalent to polymer containing copper S-hydroxyquinolate in resistance to heat degradation and is superior in yarn whiteness, making the polymer suitable for the production of textile yarns. It is also observed that yarns containing the copper phthalate may be bleached satisfactorily without excessive degradation due to catalytic action of copper which is normally to be expected with copper containing polymers. Also as shown in Example II, resistance to degradation from exposure to light is greatly enhanced by the addition of the copper isophthalate.

EXAMPLE III Copper orthophthalate is prepared following the procedure given in Example I for the preparation of copper isophthalate.

Polyhexamethylene adipamide is prepared in an autoclave in the conventional manner from 22.6 lbs. of an aqueous salt solution containing 48.6% by weight of hexamethylen'ediammonium adipate. When the autoclave temperature reaches C., 9.08 grams of potassium iodide in 100 ml. of water is added and when the temperature reaches C., 0.908 gram of copper orthophthalate dispersed in 50 ml. of water is added. On completion of the polymerization cycle, the polymer is extruded, cooled, and cut into flake in the conventional manner. The flake which has a relative viscosity of 40 is melted in a screw melter, passed at a rate of 2 lbs./ hr. through a spinneret assembly having a /2" diameter sand pack and extruded to form filaments. The extruded filaments are quenched, drawn, and wound into a yarn in the conventional manner. Analysis of the yarn indicated 0.18% by weight of potassium iodide and 50 p.p.m. by weight of copper. Heat aging tests were carried out on the yarn as described in Example I. Results of these tests are shown in Table IV below in comparison with other yarns, the preparation of which is described below.

To illustrate the superiority of the yarn of this invention as compared to yarns which are merely coated with an antioxidant containing material as disclosed by Kuhn et al. in US. 2,790,734, the following yarns were prepared. Emulsion type padding baths having the proportions of constituents as set forth in the following tables and which are the same as those used by Kuhn et al. in his Example 4, with substitution of copper orthophthalate for copper stearate of that example, were prepared.

TABLE II (COATING No. 1)

Parts by weight TABLE III (COATING N0. 2)

Parts by weight Butylated melamine-formaldehyde condensate 1.6 Ethyl cellulose (10 cps. standard ethoxy) 1.8 Copper orthophthalate 0.4 Xylol 2.2

Emulsifying agent (phenoxy end-capped polyethylene oxide sold commercially as Igepal Co-880) 1.2 Dibutyl phthalate 0.25 NH OH 0.15 Water 91.3

Three hundred yards of 210 denier, 66-filament 66 nylon yarn was wound on a swift and coated with the.

emulsion type padding bath having the composition set forth in Table II, the coating material being brushed thoroughly onto the yarn on all sides including the part in contact with the swift. Similarly, a second 300 yards of the yarn was coated with the composition set forth in Table III above. The coated yarns were heated for 4 minutes in an oven at 180 C. (356 F.) and then wound into cones. When the yarns were analyzed for copper content, the yarn with coating No. 1 was found to have 860 ppm. by weight of copper and the yarn with coating No. 2 was found to have 1,440 ppm. of copper. These yarns were subjected to heat aging tests as described in Example I, the results being shown in Table 1V below in comparison with the yarn of this invention prepared as described above.

TABLE IV Percent strength loss in 180 C. forced air oven Also for comparison, ultraviolet exposure tests were carried out using a Fadometer with a white background as specified in Kuhn et al. with the results shown in Table V.

TABLE V Percent strength loss in Fadometer carbon are 45 hrs. 92 hrs.

Control 35 50 50 p.p.m. cu. in polymer...

Coating No. 2

It was also observed that the copper orthophthalate cannot be satisfactorily added to the polymer in the manner described in the absence of the potassium iodide since the copper compound, when added by itself, de composes to give the polymer an undesirable Blue-Violet color.

Many equivalent modifications will be apparent to those skilled in the art from a reading of the above without a departure from the inventive concept.

What is claimed is:

1. A fiber comprising a synthetic linear polycarbonamide wherein recurring carbonamide linkages are an integral part of the polymer chain containing homogeneously dispersed throughout from about 0.05% to about 0.5% based on the weight of the said polycarbonamide of an alkali metal iodide and from about 0.005% to about 0.5 by weight based on the weight of the said polycarbonamide of a copper salt selected from the class consisting of copper isophthalate, copper orthophthalate, and copper terephthalate.

2. Claim 1 wherein said alkali metal iodide is selected from the class consisting of sodium iodide and potassium iodide and said copper salt is copper isophthalate.

3. Claim 2 wherein the said polycarbonamide is a melt blend of -90% by weight polyhexamethylene adipamide and 20-10% by weight polyhexamethylene isophthalamide.

4. Claim 1 wherein said alkali metal iodide is selected from the class consisting of sodium iodide and potassium iodide and said copper salt is copper orthophthalate.

References Cited UNITED STATES PATENTS 2,705,227 3/1965 Stamatoff 26045.75 2,790,734 4/1957 Kuhn et al. 26045.75 3,272,773 9/1966 Edison et al. -a 26045.75

DONALD E. CYAJA, Primary Examiner V. P. HOKE, Assistant Examiner US. Cl. X.R. 

